Systems for apparatuses formed of light emitting devices. Solutions for controlling the off-state appearance of lighting system designs is disclosed. thermochromic materials are selected in accordance with a desired off-state of an LED device. The thermochromic materials are applied to a structure that is in a light path of light emitted by the LED device. In the off-state the LED device produces a desired off-state colored appearance. When the LED device is in the on-state, the thermochromic materials heat up and become more and more transparent. The light emitted from the device in its on-state does not suffer from color shifting due to the presence of the thermochromic materials. Furthermore, light emitted from the LED device in its on-state does not suffer from attenuation due to the presence of the thermochromic materials. Techniques to select and position thermochromic materials in or around LED apparatuses are presented.
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1. A structure comprising:
a semiconductor light emitting device having an on-state and an off-state;
a phosphor layer disposed on the semiconductor light emitting device; and
a thermochromic layer disposed on the phosphor layer, the thermochromic layer comprising a pigment having a transparent liquid state at a first temperature and a colored solid state at a second temperature lower than the first temperature, the pigment configured to transition from the colored solid state to the transparent liquid state within 250 milliseconds of the semiconductor light emitting device being switched from the off-state to the on-state,
wherein the pigment is a leuco dye.
10. An apparatus comprising:
a camera; and
a camera flash unit comprising:
a semiconductor light emitting device having an on-state and an off-state;
a phosphor layer disposed on the semiconductor light emitting device; and
a thermochromic layer disposed on the phosphor layer, the thermochromic layer comprising a pigment having a transparent liquid state at a first temperature and a colored solid state at a second temperature lower than the first temperature, the pigment configured to transition from the colored solid state to the transparent liquid state within 250 milliseconds of the semiconductor light emitting device being switched from the off-state to the on-state,
wherein the pigment is a leuco dye.
4. The structure of
8. The structure of
11. The apparatus of
13. The structure of
17. The structure of
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The present application is a continuation of U.S. patent application Ser. No. 17/028,926, filed Sep. 22, 2020, which is a continuation of U.S. patent application Ser. No. 15/747,076, filed Jan. 23, 2018, now U.S. Pat. No. 10,797,206, which is a U.S. National Stage Entry of International Application No. PCT/US2016/039782, filed Jun. 28, 2016, which claims the benefit of priority to U.S. Provisional Application No. 62/196,178, filed Jul. 23, 2015. Each of the above patent applications is incorporated herein by reference in its entirety.
This disclosure relates to an apparatus formed of light emitting diode (LED) devices, and more particularly to techniques for varying the off-state color of a light emitting apparatus.
When in an off-state, light emitting devices such as light emitting diodes (LEDs) show as the color of phosphors that have been applied on the top of the LED chips. The phosphor might serve the purpose of downconverting light, however the color of the phosphor does not necessarily match a designer's desired color, and does not necessarily match the color of the emitted light when the light emitting device is in an on-state. Accordingly, it is often desired to manage the off-state color of the LED for cosmetic reasons. An example is a translucent diffusive layer applied over the LED of, for example, a flash unit in order to provide a white off-state appearance. Further control of the off-state appearance has long been desired so as to be flexible with respect to controlling cosmetic appearances of a finished product.
Typical white LEDs consist of LED chips covered by wavelength converting materials such as phosphors, dyes, or quantum dots. Because of this structure, phosphors are visible when the LED is powered off. Yellow- or orange-looking phosphors are often visible. Further, yellow or orange appearances might be aesthetically in conflict with a designer's intention. For this reason, a white diffusive layer is often applied to the flash units. Such diffusive layers are limited to white light (translucent) to minimize the optical disadvantages such as the emission color being chromatically skewed and/or the emission light intensity being decreased.
Improvements are needed.
According to certain embodiments of the herein-disclosed techniques for controlling the off-state appearance of a light emitting device, a method and apparatus are used in systems that dispose thermochromic materials of a selected color onto visible portions of the apparatus.
Certain embodiments are directed to technological solutions for disposing thermochromic materials of a selected color onto the apparatus, which embodiments advance the relevant technical fields as well as advancing peripheral technical fields. The herein-disclosed techniques provide technical solutions that address the technical problems attendant to lighting system designers who want to control the off-state appearance of designs without introducing color shifting of the output light and without suffering decreased light output in the on-state.
Some embodiments comprise a structure or derive from a structure comprising a semiconductor light emitting device and thermochromic pigment that is disposed in a path of light emitted by the semiconductor light emitting device. Some variations further comprise disposing a wavelength converting material between the semiconductor light emitting device and the thermochromic pigment.
In some variations the thermochromic pigment is in direct contact with the wavelength converting material.
In some variations the thermochromic pigment is spaced apart from the wavelength converting material, which variations can further comprise a heat generator in direct contact with the thermochromic pigment, and some variations further comprise electrically-conductive wires embedded in the thermochromic pigment and/or disposed on or embedded in a conductive glass.
Some variations further comprise a lens disposed in a path of light emitted by the semiconductor light emitting device, wherein the thermochromic pigment is disposed on the lens. In some variations the thermochromic pigment is disposed in a transparent material.
In example variations, the thermochromic pigment undergoes a phase transition by heating, wherein during the phase transition the thermochromic pigment changes from a colored appearance to a transparent or translucent appearance. The colored appearance is one of blue, or black, or red.
Some embodiments are fabricated by practicing a method for forming a semiconductor light emitting device and for disposing thermochromic pigments in a path of light emitted by the semiconductor light emitting device. Method steps can further comprise heating the thermochromic pigment to a temperature such that the thermochromic pigment undergoes a phase transition. The heating can include positioning the thermochromic pigment such that the thermochromic pigment absorbs heat generated by the semiconductor light emitting device or the heating can include activating a heat generator to heat a thermally-conductive structural member that is in contact with the thermochromic pigment.
Further details of aspects, objectives, and advantages of the technological embodiments are described herein and in the following descriptions, drawings, and claims.
The drawings described below are for illustration purposes only. The drawings are not intended to limit the scope of the present disclosure. Like reference characters shown in the figures designate the same parts in the various embodiments.
Some embodiments of the present disclosure address the problem of controlling the off-state appearance of lighting system designs such that color shifting of the output light in the on-state is eliminated or reduced and such that light output in the on-state is not unduly attenuated. Some embodiments are directed to approaches for selecting an off-state color of thermochromic materials, and then controlling thermochromic materials through transitions from an on-state of a lighting system to the off-state of the lighting system and back. The accompanying figures and discussions herein present example structures, devices, systems, and methods.
In embodiments of the present invention, an LED's off-state appearance may be changed from the typical phosphor-coated appearance. In some embodiments, the off-state appearance is changed without losing any LED functionality, or without losing any substantial LED functionality. By applying heat-sensitive pigments (called thermochromic materials) over the LED, the off-state appearance of the LED is defined by the heat-sensitive pigments (e.g., red, green, blue, etc.) or combinations of pigments (e.g., mixtures that combine to a black color, mixtures of green and blue pigments, etc.). When the LED is powered on, heat generated by the LED apparatus causes a phase transition of the thermochromic materials into a transparent/translucent state such that normal light emission from the LED is achieved. Thermochromic pigments can also be spaced apart from the LED by implementing a separate heat generator to cause the phase transition of the thermochromic pigments, or by designing a structure where the temperature of the pigments is raised to the temperature necessary for the phase transition by absorbing light from the LED.
Various embodiments are described herein with reference to the figures. It should be noted that the figures are not necessarily drawn to scale and that elements of similar structures or functions are sometimes represented by like reference characters throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the disclosed embodiments—they are not representative of an exhaustive treatment of all possible embodiments, and they are not intended to impute any limitation as to the scope of the claims. In addition, an illustrated embodiment need not portray all aspects or advantages of usage in any particular environment. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated. References throughout this specification to “some embodiments” or “other embodiments” refer to a particular feature, structure, material or characteristic described in connection with the embodiments as being included in at least one embodiment. Thus, the appearance of the phrases “in some embodiments” or “in other embodiments” in various places throughout this specification are not necessarily referring to the same embodiment or embodiments.
Some of the terms used in this description are defined below for easy reference. The presented terms and their respective definitions are not rigidly restricted to these definitions—a term may be further defined by the term's use within this disclosure. The term “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application and the appended claims, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or is clear from the context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A, X employs B, or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. As used herein, at least one of A or B means at least one of A, or at least one of B, or at least one of both A and B. In other words, this phrase is disjunctive. The articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or is clear from the context to be directed to a singular form.
Reference is now made in detail to certain embodiments. The disclosed embodiments are not intended to be limiting of the claims.
The chart shows a heating path 130 that traverses through time and temperatures corresponding to a colored state 110, a phase transition 112, and a transparent state 114. The shown temperatures and temperature ranges are merely examples of certain thermochromic materials that change color and transmittance as a function of temperature. When thermochromic materials are placed in proximity of a light emitting diode (LED), and the proximal light emitting diode is turned on, then the temperature of such materials increases over time (see the abscissa of the chart). An apparatus such as an LED lamp or flash unit can be constructed such that thermochromic materials that are placed in proximity of a heat-generating light emitting diode change phase. One phenomenon of thermochromic materials is to change visual appearance as the materials transition between phases.
Thermochromic materials are often based on either liquid crystals or leuco dyes. Liquid crystals are used in applications where the liquid crystal responses are used within relatively narrow ranges of temperatures.
Regarding liquid crystal responses, color changes result from changes of reflectivity of certain wavelengths by the crystalline structure of the material. As the crystalline structure of the material changes over a temperature range (e.g., between a low-temperature crystalline phase, through an anisotropic chiral or twisted nematic phase, to a high-temperature isotropic liquid phase) so does the apparent color. Light passing through the crystalline structure undergoes Bragg diffraction. Wavelengths with the greatest constructive interference are reflected back, which in turn gives off a colored appearance. Changes in the temperature of the material can result in changes of spacing between the crystalline layers and therefore changes in the reflected wavelengths. The apparent color of a thermochromic liquid crystal can range from non-reflective (e.g., black), through the spectral colors, and into a transparent regime. The color, reflectance, and transparency can vary depending on the temperature.
Regarding leuco dyes, such dyes are often used in applications that demand a wide range of colors to be used and/or when response temperatures need not be precise.
Considering the depiction of
When power to the LED lamp is turned off, the thermochromic materials begin to cool, following cooling path 140. After a phase transition of the thermochromic materials, the bulb begins to appear with a color.
The on-state can be maintained for any duration (e.g., while power is applied to the LED so as to raise the temperature), and the off-state can be maintained for any duration (e.g., while power to the LED is off so as to allow the temperature to decrease to an ambient temperature). A series of state transitions responsive to transitioning events is shown and described as pertains to
At state 102 (e.g., a power-off state) the solid pigment is colored. The color can be controlled by selection of pigments and other materials (see
When the phase transition is complete, and during the time period that the LED is at an elevated temperature, the liquid pigment is in a state 106 that remains transparent to the light emanating from the LED. This state can be maintained while the LED is at an elevated temperature (e.g., due to being powered-on). When there is a power-off event, the decreased temperature causes a phase transition of the pigment back to a solid (see transition state 108). After a phase transition back to a solid is complete, the LED transition to the power off state, state 102, and once again the solid pigment appears as having a color.
The transition from solid to liquid and back from liquid to solid can occur in a relatively short time period. For example, the temperature of the pigment can change sufficiently fast so as to cause a phase change from solid to liquid in a fraction of a second. The following figure depicts a fast phase transition as a function of a time-variant current being applied to a proximal light emitting device.
As shown a semiconductor light emitting device 222 is formed using a submount 216, atop of which is grown n-type material 214. An active region 212 might be doped before disposing p-type material 210. Electrical contacts are formed on the n-type and p-type layers. When an electrical potential of sufficient voltage is applied to the contacts (e.g., between the n-type and the p-type material), photons are emitted from the active region. Such photons might be substantially monochromatic (e.g., blue light). Some variations of semiconductor light emitting device 222 might include a phosphor layer 208 so as to convert monochromatic photons into photons of different energies. As such, down-converting, and in some cases up-converting photons can be engineered (e.g., by selection of wavelength-converting materials) so as to produce light that ranges across a wavelength spectrum. The phosphor layer can be disposed proximal to the active region of the semiconductor light emitting device, or it can be disposed remotely, such as on an inside surface of a bulb.
A thermochromic layer 202 provides structure such that an off-state appearance may be controlled so as to be changed into a transparent appearance. Specifically, when the semiconductor light emitting device is powered on, heat generated by the semiconductor light emitting device causes a phase transition of the thermochromic materials disposed in or on the thermochromic layer such that a transparent or translucent appearance is achieved. In this and other embodiments, light emissions are achieved without light output attenuation and without undesired on-state chromatic shifting.
In some embodiments, thermochromic pigments can be disposed so as to be distal from the LED by implementing a separate heat generator (e.g., heating element 2181, heating element 2182) so as to cause the phase transition of the thermochromic pigments by heating, or by designing a structure where the temperature of the pigment is raised to the temperature necessary for the phase transition by absorbing photons from the LED. In some embodiments, a densified film of thermochromic pigments is used to enhance heat transfer from the LED to all pigment particles. Thermochromic pigments may be applied to a surface of electrically-conductive and/or thermally-conductive glass such as is shown in
In some embodiments of the invention, thermochromic pigments are applied on top of LEDs in a thermochromic pigment layer 206 on top of a phosphor layer 208 that is disposed in an optical path of the LED active region.
Thermochromic pigments are often available in powder forms and in different colors. In many cases, thermochromic pigments of various colors are selectable based on specific phase transition temperatures.
There are many possible ways of disposing the thermochromic pigments in the optical path of the LEDs such that the thermochromic pigments are heated during operation of the LED or heating element. Thermochromic pigments 232 can be applied on a secondary optic such as, for example, a lens 230. The thermochromic pigments applied to the lens absorb light emitted by the LED when the LED is powered on. The absorption of photons from the LED raises the temperature of the lens as well as the thermochromic material, which raised temperature serves to push the thermochromic material through a phase change which in turn exhibits transparency or translucence.
In any of the foregoing embodiments, heating the thermochromic pigment to raise the temperature can include any combinations of heating by operation of the LED, and/or by activating a heat generator that is thermally coupled to the thermochromic pigment (e.g., by proximity, or due to presence of the thermochromic pigment in or on a thermally-conductive structural member).
A device such as is depicted in the foregoing
A given application many include a variety of design requirements that can influence selection of a pigment. Strictly as an example, a selection chart can be used so as to facilitate choices when mixing colored and black pigments.
The chart also depicts class 304 and class 306, where green and/or blue thermochromic pigments are mixed with phosphors of red, orange or yellow phosphors so as to produce a desired hue, intensity, and tint, possibly to match to a reference color (e.g., for aesthetic purposes). Blue and black thermochromic pigments exhibit similar switching time characteristics. The class 308 depicts a choice of adding blue or black pigments to mix with other pigments and phosphors offers a wide range of color choices that can be applied to an LED apparatus so as to exhibit a wide range of colored off-state appearances.
The chart depicts switching temperatures from relatively lower temperatures to relatively higher. The shown class 3101 depicts relatively lower switching temperatures while class 3102 depicts relatively higher switching temperatures.
ThermoChromic Capsules
Thermochromic pigments are often delivered as capsules that comprise a dye, (e.g., a spirolactone, a spiropyran or a fluorane) that forms a colored complex with a developer (e.g., a phenolic-compound such as bisphenol-A). The dye and the developer are both present within sealed polymeric capsules that are filled with a long chain alcohol, ester or acid. The melting point of the alcohol, ester or acid determine the switching temperature of the dye. Upon melting, the dye-developer complex dissociates, thus leading to discoloration of the material. Melamine or other polymers that are hard and relatively temperature stable polymers are often used for the polymeric shell.
As earlier mentioned, it is desired that the thermochromic materials exhibit a high degree of reflectivity (e.g., of the sought-after color) when in the solid state, and a high degree of transparency when in the liquid state. The following
In this example, the general shape of the curves demonstrates that the variation in transmittance between the two temperatures is greater at relatively lower wavelengths (e.g., in the blue-green regime). At higher wavelengths (e.g., in the orange-red regime) the thermochromic pigment exhibits higher and higher transparency.
The shown heating transition 402 starts at a low point in the spectrum and then goes through a temperature change up to 150° C. In a cooling transition 404 the material returns an earlier temperature and earlier state (e.g., the dashed line). The shown transitions are merely example transitions.
Photochemical Degradation
Photochemical degradation most often involves reactive oxygen species such as singlet oxygen and/or radicals originating from peroxides. Remediation techniques (e.g., techniques to inhibit oxygen-related degradation) include introducing antioxidants and radical scavengers such as hindered amine light stabilizers (HALS). Another way to inhibit photochemical degradation is to exclude oxygen from the system by the application of hermetic sealing layers on the layer or layers comprising the thermochromic capsules or on the thermochromic capsules themselves. Thin layer deposition offers a technique to protect an underlying layer or material from coming in contact with oxygen-containing gasses (e.g., air) and/or oxygen-containing liquids (e.g., water).
Further details regarding general approaches to thin layer deposition are described in co-owned patent application publication WO2016041838.
Different applications admit of different degradation remediation techniques. Strictly as an example application, a flash unit (e.g., for a camera) is hereunder discussed. Specific usage patterns and reliability requirements include:
To achieve such stringent reliability requirements, contact between the thermochromic materials and oxygen is to be avoided
Degradation Remediation through Exclusion of Oxygen
To demonstrate the effect of the exclusion of oxygen on degradation, switching in an air atmosphere (e.g., in a relatively oxygen-rich atmosphere) is compared to switching in a nitrogen atmosphere (e.g., relatively oxygen-poor atmosphere).
When the flash unit system is exposed to blue light in an air-filled environment, the transmitted intensity at high temperature decreases over time (see decreasing trend 505). The damped shape of the curve 504 indicates incomplete switching between phases and/or or browning effects. In the specific example of
Degradation of the thermochromic material can be stopped or slowed by eliminating oxygen from the environment in which the thermochromic material is disposed. One technique to eliminate oxygen is to provide a nitrogen-rich atmosphere so as to purge oxygen. Evidence of reduced performance degradation is shown and discussed as pertains to
The figure depicts two lamps that are plotted at ends of a blue-green color spectrum. One lamp exhibits a relatively longer wavelength color 606 due to a green-appearing coating of thermochromic material being applied to a body formed of a translucent material 603GREEN. Another lamp exhibits a relatively shorter wavelength color 604 due to a blue-appearing coating of thermochromic material being applied to a body formed of a translucent material 602BLUE. When a lamp is powered on, photons from the LED strike the coating, causing a phase change of the coating, which in turn causes a color and/or transmittance change. As shown, the powered-on lamp has a clear or white appearing power-on state 608, which may or may not be visible to the naked eye depending on the intensity of the emanated light.
Applications other than illumination lamps and camera flash units can avail of the herein-disclosed techniques. Strictly as additional examples, thermochromic materials can be used in filament LED lamps and/or hand-held or head-mounted flashlights and/or automotive LED headlamps and/or any applications where the LED module (specifically a coating on a portion of the LED module) is visible to the consumer.
As shown, a flash unit apparatus is integrated into a device 702 such as a smartphone or camera. In an off-state the flash unit apparatus has a green appearance (see green state 704GREEN). During a power-cycle to an on-state, the thermochromic materials in or on the visible structures of the flash unit apparatus transition to a clear state (see transparent state 704TRANSPARENT). As such, the light emanated from the flash unit apparatus is not attenuated, and is not color shifted.
Any of the disclosed embodiments or variations thereof can be used in a wide range of lighting applications and/or installation. What follows is a depiction and discussion of some example lighting applications in representative installations.
What has been described are approaches for using thermochromic materials of a selected color in LED-based illumination products together with their pertinent advantages.
Having described the invention in detail, those skilled in the art will appreciate that, given the present disclosure, modifications may be made to the invention without departing from the spirit of the inventive concepts described herein. Therefore, it is not intended that the scope of the invention be limited to the specific embodiments illustrated and described.
Masui, Hisashi, Shimizu, Ken, Bhardwaj, Jyoti, Shchekin, Oleg, Bohmer, Marcel, Jin, Frank
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